Measurement is a fundamental feature for a mobile device in mobile communication systems such as LTE since it enables a mobile device to properly attach or handover to a cell for wireless communication, but also enables a base station to estimate the channel fading and select suitable resource and modulation and coding scheme to fulfill the quality of service (QoS) requirement of mobile devices with reasonable resource. Therefore, accurate measurements constrained by limited time are essential for mobile communications.
Some system information and related configurations will impact the performance of measurement, for example, system or measurement bandwidth, transmit antenna configuration, multicast-broadcast single frequency network (MBSFN) configuration in LTE systems, and uplink/downlink configuration in time division duplex (TDD) systems, etc. This information may be informed to the mobile device by base stations via system information messages sent via a broadcast channel. For a mobile communication system the system information is standardized, for example for an LTE system in 3GPP TS 25.331. However, in some scenarios, system information is unknown to the mobile device when performing measurements, for example, initial cell search/measurements where no system information has yet been decoded, and gap-based neighbor cell search/measurements where the mobile device is connected to a non-LTE based network and is trying to measure the LTE network—in which such system information may or may not be available or accessible to mobile devices.
Without system information knowledge, such as bandwidth, transmit antenna configuration, and uplink/downlink configuration, mobile devices have to turn to a conservative way by assuming a system configuration that corresponds to the minimum system configuration of a specific radio access technology. For example, in an LTE system, the mobile device will assume a 1.4 MHz bandwidth, one transmission antenna, and only subframe 0 and subframe 5 can be used for measurement in case of Time Division Duplex, which is the minimum system configuration of LTE and contains the minimum number of reference subcarriers as disclosed in 3GPP TS 36.211. Since measurement accuracy is highly related to the number of reference subcarriers carrying reference symbols utilized, such a conservative measurement may lead to either a much longer measurement time—which is not allowed in some scenarios and costs power—or performance degradation which may reduce the margin or even not fulfill the requirements of standard. Furthermore, it will be worse if MBSFN information is unknown. In this case, since the mobile device does not know if the measured sub-frame is an MBSFN sub-frame, a performance degradation is unavoidable for a given limited measurement time.